1. Field of the Invention
The present invention is directed to a semiconductor substrate treating method, a semiconductor component and an electronic appliance.
2. Description of the Prior Art
In recent years, the requirement for higher degree of integration of devices makes a strong demand for increased cleanliness of the surface of semiconductor substrates (semiconductor wafers).
Presence of particulate contaminants such as silicon particles, dusts or the like (collectively referred to as “particles”) on the surface of the semiconductor substrates may cause disconnection or short-circuit of a device wiring. In the meantime, contamination of the semiconductor substrate surface with metal-based contaminants inclusive of transition metal may give rise to problems such as creation of oxide-induced stacking fault and shortened life time. For that reason, cleaning is conducted to remove these contaminants from the semiconductor substrate surface, in which cleaning process care should be taken to avoid re-contamination.
Examples of the conventional methods for cleaning a semiconductor substrate include: (1) cleaning the substrate with an aqueous solution of dilute hydrofluoric acid; (2) cleaning the substrate with an aqueous solution of the mixture of hydrogen peroxide and hydrochloric acid or sulfuric acid; and (3) cleaning the substrate with an aqueous solution of the mixture of ammonia and hydrogen peroxide. Used as a cleaning fluid in these methods are chemicals or water of high purity from which particulate contaminants and metal-based contaminants were eliminated as much as possible.
Among the prior art cleaning methods noted above, method (1) exhibits an excellent ability to remove or dissolve such contaminants as oxides but has a difficulty in reducing particulate contaminants. Furthermore, with respect to a semiconductor substrate having an oxide film, method (1) shows low selectivity between oxides targeted for removal and oxide films to be survived intact, as a result of which a problem is posed in that not only the target oxides but also the oxide films are dissolved or etched away unintentionally.
Method (2) takes advantage of the enhanced ability of the cleaning solution to dissolve metal-based contaminants but has no capability of dissolving oxides.
Thanks to its action to dissolve silicon per se, method (3) is capable of effectively removing particulate contaminants, resist residues and etching reaction products that subsist on the substrate. However, method (3) has a tendency to introduce metal-based contaminants into the cleaning fluid, which increases the possibility of re-contamination of the semiconductor substrate in the cleaning process. Additionally, it is known that method (3) tends to dissolve metal of high melting point, such as W (tungsten), and roughen a silicon substrate surface to thereby increase roughness thereof, thus deteriorating the performance of semiconductor devices produced.
As a solution to the afore-mentioned problems inherent in the prior art methods, what is called a “slight etching method” has been proposed whereby a semiconductor substrate (silicon wafer) is cleaned by soaking it into an aqueous solution of the mixture of 60 wt % of nitric acid and 0.1 wt % or less of hydrogen fluoride. Reference is made to, for example, an article, Rituo Takizawa, et al., “Extended Abstracts of Solid State Devices and Materials,” 1988, P. 475. In view of the fact that ultra-pure nitric acid graded for semiconductor use contains metal-based contaminants, e.g., Al, Ca, Cu, Fe, K, Na and Za, on the order of ppb or sub-ppb, the concentration of the metal-based contaminants remains significantly high in the cleaning fluid that contains as much nitric acid as 60 wt %. Moreover, in case of using a cleaning bath made of quartz glass, metallic impurities are eluted from the quartz glass bath and thereby further increase the concentration of the metal-based contaminants. Owing to the strong oxidizing action exercised by nitric acid of increased concentration, an oxide film is formed on the surface of the semiconductor substrate, in which process the metal-based contaminants present in the cleaning fluid are apt to infiltrate into the oxide film. This means that the slight etching method also has a limit in cleaning silicon wafers with a high degree of cleanliness.
In addition to the above, there has been proposed a cleaning method that makes use of, as a cleaning fluid, an aqueous solution containing no less than 0.10 wt % of hydrochloric acid, 0.05 to 10 wt % of hydrogen fluoride and 0.05 to 10 wt % of hydrogen peroxide. Reference is made to, for example, JP-B No. H8-18920. In case of using this kind of cleaning fluid, however, a drawback is observed in that, as with the aqueous solution of dilute hydrofluoric acid, the oxide films to be survived intact are dissolved unintendedly. Furthermore, this cleaning fluid has a property of dissolving high melting point metal, such as W (tungsten), and therefore cannot be employed in cleaning semiconductor substrates that comprise high melting point metal as their elements (e.g., semiconductor substrates having a gate electrode composed of such materials as W or the like).